[HES2013] Virtually secure, analysis to remote root 0day on an industry leading ssl-vpn appliance by Tal Zeltzer

Today most networks present one “gateway” to the whole network – The SSL-VPN. A vector that is often overlooked and considered “secure”, we decided to take apart an industry leading SSL-VPN appliance and analyze it to bits to thoroughly understand how secure it really is. During this talk we will examine the internals of the F5 FirePass SSL-VPN Appliance. We discover that even though many security protections are in-place, the internals of the appliance hides interesting vulnerabilities we can exploit. Through processes ranging from reverse engineering to binary planting, we decrypt the file-system and begin examining the environment. As we go down the rabbit hole, our misconceptions about “security appliances” are revealed.

Using a combination of web vulnerabilities, format string vulnerabilities and a bunch of frustration, we manage to overcome the multiple limitations and protections presented by the appliance to gain a remote unauthenticated root shell. Due to the magnitude of this vulnerability and the potential for impact against dozens of fortune 500 companies, we contacted F5 and received one of the best vendor responses we’ve experienced – EVER!

Audio available here :
More information about the conference : http://2013.hackitoergosum.org/presentations/Day1-04.Virtually%20Secure,%20Analysis%20to%20Remote%20Root%200day%20on%20an%20Industry%20Leading%20SSL-VPN%20Appliance%20by%20Tal%20zeltzer.mp3
https://www.hackitoergosum.org

Transcript

1. Virtually Secure a journey from analysis to remote root 0day on an industry leading SSL-VPN appliance
2. Who am I ? Tal Zeltzer Independent security researcher from Israel • Reverse engineering (mostly embedded systems) • C/C++ And Python development • Zerodays (Adobe Flash, PcAnywhere, EMC Networker, Windows Briefcase,…) • No formal education
3. The research • We were interested in exploiting an old vulnerability on an F5 product called FirePass. • Overview (Taken from F5.com): The FirePass® SSL VPN appliance and Virtual Edition (VE) provide secure remote access to enterprise applications and data for users over any device or network. FirePass ensures easy access to applications by delivering outstanding performance, scalability, availability, policy management, and endpoint security. The result is unified security enforcement and access control that increases the agility and productivity of your workforce.
4. Virtual “Private” Network
6. Note F5 stated that a new SSL-VPN appliance is available and the FirePass SSL-VPN appliance is supported for legacy purposes.
7. Note Combined net worth of 3 companies running this product is 177 billion dollars
8. Advantages of using a virtual appliance vs a normal appliance • Runs on x86/x64. • Kernel debugging. • Software encryption.
9. Disadvantages of using a virtual appliance vs a normal appliance • Incorrect analysis. • Different internal implementation. • Maintenance issues. • Can’t develop memory corruption exploits.
10. Downloading the vulnerable version • Download • Boot • Activate
11. 0day research • We can’t work with the vulnerable version. • We can only try and find 0days now…
12. Attack surface (Black box) • Open ports: http, https, ssh. • Mostly PHP based. • This will be our main attack vector for now.
13. Getting a debug-shell • Extract PHP files. • Examine configuration. • Other attack vectors?
14. The “debugStub” feature • Remote kernel debugging. • Use GDB to kernel debug. • Unknown kernel version.
15. Mounting the drive in a different OS • Boot partition. • Hard drive encryption. • Losetup, GPG, rootkey.gpg. • Unable to mount the encrypted drives.
16. The boot partition
17. Interacting with the boot process • Replaced losetup with a busybox shell. • Booted and got a shell! • Broke the decryption process.
18. The limited shell
19. Decrypting the file-system • During the normal boot process we noticed a command “/lib/losetup –e …” • Decrypted the file-system.
20. Getting a debug shell • Compiled a backdoor. • Added it to “init.rd”. • Rebooted and got a debug shell on our local appliance.
21. Attack Surface (White box) • Distribution: • OpenSSL: • Apache: • … Slackware 7.1 (June 22, 2000) 0.9.7d (March 17, 2004) 1.3.33 (October 29, 2004)
22. Attack Surface (White box) • Vulnerable applications. • Known vulnerabilities. • Unknown architecture. • Hard to write a reliable memory corruption exploit without a test box.
23. Attack Surface (White box) • Unknown apache modules. • SSH is modified. • Downloaded the PHP scripts.
24. PHP Scripts
25. Character distribution
26. PHP Scripts • Character distribution is flat. • No compression headers. • Probably encrypted.
27. PHP Scripts • Found several PHP code obfuscation and encryption solutions. • Found one of them on the appliance (“IonCube"). • Found a talk by Stefan Esser that explained the situation.
28. Closed source PHP scripts • This solution pre-compiles and encrypts the PHP code. • A solution exist (Xdebug / VLD) • Since this is an old version of “IonCube” it should work.
29. Xdebug / VLD • Hard to compile. • Dropped this angle for now; If everything fails we’ll go back and try it.
30. Setting up the environment • Trying to install tools. • Installed GCC, SSH, and others. • Enabled mysql log • Decided to have another look at the unknown apache modules
31. MySQL Log
32. Custom apache modules • Found a custom apache module that maps to a virtual directory
33. Analyzing the virtual directory • Immediately launched a browser and tried to access the directory. • Got a “Invalid parameters” error. • Found the tunnel-handler. • Launched a disassembler
34. Playing with the parameters • We already have mysql log enabled. • While playing with the parameters we found an SQL injection vulnerability.
35. SQL Log When we provide hello’ as the ‘sess’ parameter we get:
36. Writing into outfile • When writing into outfile a common query looks like this: hello’ union select ‘data’, ‘x’ into outfile ‘/tmp/test’-- Select logon, usergroup from tblLogSessions where lower(sid) = lower(‘hello’) union select ‘data’, ‘x’ into outfile ‘/tmp/test’-- ‘)
37. Trying to SQL inject • When sending the query string “aaa%20” We get “aaa%20” at the actual query • Turns out that url-encoded strings are not decoded :/
38. Trying to SQL inject • When sending the query string “aaa%20aaa” We get “aaa 0x1.d42…” at the actual query. • We got a format string vulnerability at the same argument! (Disassembly confirmed)
39. The format string • Just to be sure, let’s send the query string “%08x--%08x--%08x…” • That’s nice but we already have a logical vulnerability; I want a universal exploit!
40. Trying to SQL inject • Turns out that the apache module doesn’t escape the url-encoded query string. • Can’t write characters such as space • How can we write a valid query?
41. Trying to SQL inject • Block comments? • A query like “Or/**/1=1/**/)” worked! • What about the rest of the query? • -- doesn’t seem to work without a trailing space hello’/**/union/**/select/**/‘data’,/**/‘x’/**/into/**/outfile/**/ ‘/tmp/test’--
42. Trying to SQL inject • Documentation confirmed “--” has to have a trailing space • Format string you say? Spaces you say? What about %20d ? • Got our valid terminator! hello’/**/union/**/select/**/‘data’,/**/‘x’/**/into/**/outfile/**/ ‘/tmp/test’--%20d
43. Writing into outfile • Composed our union select into outfile; Failed. • But everything looks fine.
44. Wtf? • Tried running the query myself; Failed. • Tried a trivial union select; Failed.
45. Mysql 3.23 • No union selects. • No nested queries. • Can’t do a join because we’re at the while condition. • Can write into outfile, but since there’s no union we do not control the data that gets written. hello‘/**/or/**/ (‘1’=‘1’)/**/into/**/outfile/**/’/tmp/test’/**/--%20d
46. The table we write into outfile • tblLogSessions; Contains session info. • Updated when we login successfully. • Can’t poison it because we can’t login.
47. Really getting mad • Read documentation. • Read some source code. • Asked anyone I know. • And then!
48. Got it
49. Writing into outfile! • Can write arbitrary data into the file. • What about ‘<?php $mycode ?>’. hello‘/**/or/**/(‘1’=‘1’)/**/into/**/outfile/**/’/tmp/test’/**/ fields/**/seperated/**/by/**/0x603c3f706870…3f3e /**/--%20d
50. Pwned!
51. Minor down-side • This attack will only work if a user or an administrator has ever logged in to the server • I’m guessing it’s not much to ask in a production environment (Initial server configuration applies as a login)
52. Got root ? • Rootkit the appliance. • Sniff traffic. (tcpdump is available) • Man-in-the-middle VPN clients • Extract certificates • Create our own user and join the network
53. Attacking VPN Clients • Replace existing PHP scripts (can’t edit them..) • If ActiveX installation fails we get a “please download and install this client” message. • New client anyone?
54. F5 – Vulnerability response win • From all my vulnerability disclosures F5 impressed me the most. • Their response was quick and professional. • The patch came soon after. • F5 wants to work with all researchers. Contact them at security-reporting@F5.com.
55. Live Demo
56. I’m wrong!
57. I’m wrong!
58. The real PHP encryption • Turns out the “IonCube” module is just for PHP acceleration. • The encryption is RC4 implemented at the PHP “lexer” level.
59. Long story short
60. Thanks to the EFF • Many many thanks to the EFF and marcia hofmann for their legal consulting and help.
61. Greets and Thanks • Mati aharoni (Aka muts) – Configuring linux and highlighting some critical points • Oran avraham – Ninja, helping me out with linux stuff and solving huge problems in seconds • Igor Rayak, Shai Priel, UY, Yuval Ofir, m0she, Gil Dabah, Assaf Nativ
62. Questions?